1. Field of the Invention
A method and apparatus for inferring the existence of light is disclosed. The method comprises measurement of the electrical characteristics of a nanotube bound with a dye.
2. Description of the Related Art
A photoelement is disclosed by [1]. The known photoelement is a photodiode which is usually implemented on the basis of silicon or another semiconducting material.
A drawback of such a photoelement, in particular, is its relatively low efficiency, caused by its relatively nigh electrical resistance, and its relatively large footprint on a chip, as a result of which the positional resolution in particular of a photoarray comprising such a photodiode is limited.
Also known from the prior art are carbon nanotubes [2]. A typical single-wall nanotube has a diameter of about 1 nm, the length of a nanotube possibly being a few hundred nanometers. Typically, the end of a nanotube is capped, i.e. covered, by half a fullerene molecule.
Carbon nanotubes are aromatic graphite-like structures. Their extended electron system renders the nanotubes electrically conductive, which suggests that the nanotubes are particularly suitable for the construction of nanocircuits. A number of fundamental experiments have demonstrated the controllability of this conductivity of the nanotubes. Hitherto, the diameter and the chirality of a nanotube have been thought to play an important part in the character of said conductivity.
It is further known to lower the conductivity by doping a carbon nanotube with boron nitride [3].
The conductivity can also be influenced by applying an electrical field to the nanotube (so-called field effect), as described in [4].
A nanotube coupled to a dye is disclosed by [5]. According to [5], the dye coupled to the nanotube is made to chemiluminescence either by the emission of light of a suitable wavelength or by applying an electrical potential which is sufficient to excite an electron present in the dye, on the basis of which chemiluminescence the presence of biomolecules likewise bound to the nanotubes can be detected.
In addition, [6] discloses chemical derivatization of C60-fullerene molecules, and [7] discloses coupling of the latter to light-sensitive units.
Because of the growing interest in nanoswitching technology it is desirable to establish novel methods of utilizing the electrical characteristics of nanotubes.
It is therefore an object of the invention to specify a further method of inferring the existence of light by means of a measurement of the electrical characteristics of a nanotube bound with a dye.
This object is achieved by a method of inferring the existence of light by means of a measurement of the electrical characteristics of a nanotube bound to a dye. A method of inferring the existence of light by means of a measurement of the electrical characteristics of a nanotube bound to a dye first of all involves bringing a nanotube derivatized with a dye into contact with two conductor tracks. An electrical parameter of the nanotube is then measured via the two conductor tracks without exposure to light. Then the dye bound to the nanotube is irradiated, and the electrical parameter of the nanotube is then measured via the two conductor tracks with exposure to light. The difference between the value of the electrical parameter measured without exposure to light and the corresponding parameter measured with exposure to light is then established. Finally it is inferred, as a function of the difference established, whether light is present.
Photoexcitable dyes have extended, delocalized orbital systems. Coupling such a photoexcitable dye to the nanotube ensures that an incident light quantum excites said extended orbital system of the dye in such a way that an electron present therein is promoted and delocalized throughout its orbital system. Owing to the higher energy imparted to the electron by the incident light quantum, and owing to the spatial proximity of the extended orbital system of the dye to the extended orbital system of the aromatic nanotube, the electron excited in the dye is now delocalized throughout the extended orbital system of the nanotube. Said delocalization of the excited electron throughout the extended orbital system of the nanotube therefore results in a change in the electrical characteristics of the nanotube, viz. its electrical conductivity.
Monitoring of the electrical characteristics of the nanotube thus derivatized therefore, according to the invention, allows the existence of light having a wavelength suitable for exciting an electron present in the dye to be established in the surroundings of the nanotube. This allows light quanta to be detected with very high sensitivity while maintaining a size suitable for the use of nanocircuits.
The inference of the existence of light can furthermore be performed quantitatively.
The electrical response can be a change in the conductivity, in the resistance, in the capacitance or in the inductance of the nanotube.
A photoelement includes at least one nanotube whose electronic characteristics can be controlled by exposure to light. Said photosensilization of a nanotube is achieved by a bond, preferably a covalent bond, to a dye.
Such a nanotube can be fabricated by means of a method in which, in a first step, the nanotube is derivatized by the generation of chemically reactive groups and, in a second step, a photoexcitable dye is coupled to the nanotube thus derivatized. According to one embodiment of the invention, derivatization is effected at one or both longitudinal ends of the nanotube.
This further facilitates derivatization, as the ends of a nanotube, in any case, are normally more reactive than the cylindrical surface of the nanotube.
The nanotube can be a carbon nanotube or a nanotube doped with boron nitride.
In addition, the derivatization may comprise an oxidation step.
According to a further embodiment of the invention, the step of oxidizing the nanotube is to be performed by reacting the nanotube with nitric acid, sulphuric acid, persulphuric acid, perhalic acids, organic peracids, or with combinations thereof or with halogen or interhalogens.
Furthermore, oxidation of the nanotube can be carried out at room temperature or at a temperature up to the boiling temperature of the respective solution or by irradiation of the nanotube in the presence of halogen or interhalogens.
The halogenated nanotube obtained by irradiation of the nanotube in the presence of halogen or interhalogens can, according to a further embodiment of the invention, then be converted into the corresponding carboxylated nanotube. Suitable for this purpose are, for example, (CO, CO2(CO)8, NaOH, h and H+), (CO, Ca(OH)2, MeOH, catalytic PdCl2(PPh3)2), (CO, H2O, n-Bu3N, catalytic PdCl2(PPh3)2) and/or (CO2, catalytic Pd and electrolysis).
The derivatization can further comprise reaction of the carboxyl groups with a halogenating or water-eliminating reagent, thereby further continuing the derivatization process.
Examples of suitable halo-eliminating or water-eliminating reagents include SOCl2, COCl2, PCl3, PCl5, (CCl4 and Ph3P), PhCOCl, ClCOCOCl or Cl2CHOMe, or carbodiimides or mineral acids.
According to a further embodiment of the invention, coupling is effected with a dye which includes a chemically reactive group which can enter a covalent bond with the carboxyl group or with the acyl chloride, the chemically reactive group of the dye not forming part of the dye""s electron system responsible for the dye characteristics.
The dye derivative used can, for example, be aminofluorescein, a triphenylmethyl cation salt (trityl salt), a suitably derivatized porphine or hypericin.
A nanoelectric component includes at least one nanotube bound with a dye, preferably covalently bound, the electrical characteristics of the nanotube being controllable by shining light onto the one or more dye molecules.
Specific embodiments of the invention are shown in the figures and will be explained below in more detail.